Letter to my Host Family?

Hi guys!!
I would really need your help...you see I going to go on an exchange to Japan next year and now I have to write a letter to my host family...in Japanese ^^; I've already got some lines, but I'm not sure how right it is. So I'd be really thankful if you could help me and correct it ^^;

ホストファミリーへ
はじめまして, xxです. どうずよろしくおねがいします. おげんきですか.
すみませんがわたしのにほんごがあまりじょうずですからこのてがみはとてもみじかいです.
いま 17さい のがくせいです. らいねん こうこうをでて にほんにいくまえに 18さい なります.
わたしは りょうしんと xx のきた にすんでいます. xx に すんでいます. きょうだいがいません.
わたしは (shy) -くて しんせつなひとです. そして えをかくかとがだいすきです.
3ねんかんにほんごをべんきょうしています. でも にほんにいった こと が ありません がとても いきたいです.

Also I have no clue how to end the letter(I would like to thank them in andvance for taking me in and to say that I can't wait to meet them) ^^
And maybe you can give me tips on how to make the letter sound less stiff ;)

ホストファミリーのみなさんへ

It would be nicer to say "To everyone at the host family" rather than just "to host family."

はじめまして、xxです。
You don't have to say "how are you?" as first-time greeting :)

すみませんがわたしのにほんごはあまりじょうずではありませんから、このてがみはとてもみじかいです。
What you wrote said "My Japanese is good..." so I changed to negative.

いま 17さい のがくせいです。らいねん こうこうをでて にほんにいくまえに 18さい なります。
OK

わたしは りょうしんと xx のきた にすんでいます。 xx に すんでいます。きょうだいはいません。
Are you going to put state name into "xx"? City name?
For saying you don't have any brothers/sisters, you should use "wa" not "ga." You could also say ひとりっこです。to say you are the only child.

わたしは (shy) -くて しんせつなひとです。
You don't really say that you are kind yourself, that sounds a bit like boasting :) please come up with another expression :)

そして えをかくことがだいすきです。
Just a typo, I assume.

3ねんかんにほんごをべんきょうしています。でも にほんにいった こと が ありません がとても いきたいです。
OK

あうのを　とても　たのしみに　しています。
"I am very much looking forward to seeing you."

どうぞよろしくおねがいします。
Just a typo.

I am not doing any extensive editing to make it super polite or anything, as that would give your host family the wrong impression about your proficiency in Japanese :)

わたしは (shy) -くて しんせつなひとです。

As AK suggested, "わたしは しんせつ" sounds talking yourself up.
How about this?
わたしは うちき(orはずかしがりや) ですが、
したしみやすい(friendly) にんげんです。
or おんわな(mild-tempered) にんげんです。

And to put "どうぞよろしくおねがいします。" at the end is the usual phrase as closing remarks.

Thank you all very, very much for your help ^^ I don't know what I would do without you :D
Yes I would add my city name for XX :)
I'll definitely change the 'kind' part! o.O I had no clue...thanks for showing me that mistake!!! :D ...would have been very embarassing otherwise :P
And sorry for the typos ^^;
Thanks again!!!! You are the best!!!!

Oh! Another thing. If I change: わたしは りょうしんと xx (county name) のきた にすんでいます。 xx (city name) に すんでいます.
to:わたしは りょうしんと xx (city name)に すんでいます. xx (my country)のきたのまちです.
Sorry for all the questions, but I just noticed that I used the same verb twice... ^^;

わたしは りょうしんと xx (city name)に すんでいます. yy (my country)のきたのまちです.

I think these two sentences are OK.

Initially, reading "yyのきたのまちです" I somehow assumed that "xx" was a city located TO the north of some other city. But if you write your country's name, it should be clear what is located where :)

Thank you for your help agian! ^^
I really own you!!!! :D
Thaaaaannks *hug*

Just do your best. You don't need to sweat the small stuff.